What does TR mean in Excel ?

Hello guys ,An excel file is handed to me that include a column of precipitation (IN MM) that has a values like so : "1.5" , "2.2" , "0.0" , 0.1 , 0.2 , 31.4 , 177.6 , 69.5 , 22.8 , etc but the problem is one of this values is "TR" , I know it has nothing to do with aerology , so I'm wondering what the hell is that ?
Thanks ,